Hydraulic system

ABSTRACT

A variable-flow hydraulic pump has an adjusting member movable between a plurality of flow-adjusting positions. A larger and a smaller piston act upon this member at opposite sides thereof. The smaller piston is always connected with the high-pressure side of the pump. A multi-position servo-control unit is connected in circuit with the high pressure side and the lowpressure side and includes a relief valve connected with the larger piston and serving to control the flow of fluid from the high-pressure side to the same when the fluid pressure exceeds a preset limit. A control valve is connected with the high pressure side and with the servo-control unit and serves to operate at a pressure slightly below the preset limit and at this time to move the servo-control unit to a position in which the unit connects the larger piston with the high-pressure side and interrupts the communication of the larger piston with a low-pressure space.

United States Patent [191 Rometsch et al.

[ Dec. 9, 1975 HYDRAULIC SYSTEM [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Oct. 30, 1974 [21] Appl. No.: 519,101

[30] Foreign Application Priority Data Primary ExaminerWilliam L. Freeh Assistant Examiner-G. P. LaPointe Attorney, Agent, or FirmMichael S. Striker [57] ABSTRACT A variable-flow hydraulic pump has an adjusting member movable between a plurality of flow-adjusting positions. A larger and a smaller piston act upon this member at opposite sides thereof. The smaller piston is always connected with the high-pressure side of the pump. A multi-position servo-control unit is connected in circuit with the high pressure side and the low-pressure side and includes a relief valve connected with the larger piston and serving to control the flow of fluid from the high-pressure side to the same when the fluid pressure exceeds a preset limit. A control valve is connected with the high pressure side and with the servo-control unit and serves to operate at a pressure slightly below the preset limit and at this time to move the servo-control unit to a position in which the unit connects the larger piston with the high-pressure side and interrupts the communication of the larger piston with a low-pressure space.

6 Claims, 1 Drawing Figure US. Patent Dec. 9, 1975 3,924,969

HYDRAULIC SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a hydraulic system in general, and more particularly to a hydraulic system which controls the operation of a variable-flow fluidhandling machine.

It is known to provide variable-flow fluid-handling machines, for example pumps, with control arrangements which include a pressure relief valve whose purpose it is to provide for a low-loss pressure limitation of the pump or a hydrostatic drive supplied with fluid from the pump. The basic consideration behind such an arrangement is to protect the pump, the drive and the seals against overload pressures.

However, these arrangements have not been satisfactory because they also include a servo-control unit which serves to adjust the pump to thereby vary the throughput of fluid per unit time. These servo-control units, however, have tended to negate the effect of the relief valve so that the desired overload protection was not reliably obtained. Attempts to rectify the problem by arranging throttles of small cross-section in the input and output conduits connected with the servo-control unit have also not been successful because the presence of such throttles disadvantageously influences the response time of the service control unit and over a period of time the throttles tend to become clogged, thus making the servo-control unit inoperative.

SUMMARY OF THE INVENTION It is, accordingly, a general object of this invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide an improved hydraulic system of the type in question which avoids the aforementioned disadvantages.

Still more particularly, it is an object of the present invention to provide such an improved hydraulic system which fully offers overload protection without disadvantageously influencing the response time of the servo-control unit.

In keeping with these objects, and with others which will become apparent hereafter, one feature of the invention resides in a hydraulic system which, briefly stated comprises a variable-flow fluid-handling machine having a high-pressure side and a low-pressure side and an adjusting member which is movable between a plurality of flow-adjusting positions. A larger and a smaller piston act upon the member in mutually opposite directions, and the smaller piston is connected in circuit with the high-pressure side. A multi-position servo-control unit is connected in circuit with the machine and includes a relief valve in circuit with the larger piston end of the machine for controlling the flow of fluid from the high-pressure side when the fluid pressure exceeds a preset limit. A control valve is connected with the high-pressure side and with the servocontrol unit and is operative at a pressure slightly below the preset limit for moving the control unit to a position in which the unit connects the larger piston with the high-pressure side and interrupts communication of the larger piston with a low-pressure space.

The novel features which areconsidered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation,

2 together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in con-- nection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING I The single FIGURE is a diagrammatic illustration showing a system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing shows an exemplary system according to the present invention, using a fluid-handling machine 10 which will be seen to be capable as operating both as a fluid pump and as a fluid motor. For purposes of this description, the machine 10 will be described with respect to its operation as a variable flow rate pump. It has a rotor 1 1 which is mounted for rotation in a diagrammatically illustrated cavity 14 of a housing (the latter is not specifically shown) and is formed with a plurality of radially extending slots in which slot pistons or vanes 12 can slide radially inwardly and radially outwardly. The outward ends of these vanes 12 engage a control member, in the illustrated embodiment a control ring 13 which can be shifted in the cavity 14 from its one extreme position, that is illustrated in the drawing, to a plurality of other positions, thereby varying the extent to which fluid can flow through the pump per unit of time. This, therefore, is a machine of the type generally known as sliding-vane motors or pumps and its operation per se is well known.

The displacement of the member 13 thus controls the rate of fluid flow in the machine 10 between zero value and a maximum value; displacement is effected with the aid of two pistons 15 and 16 which are respectively slidably mounted in two cylinder bores 17 and 18 formed in the housing at sides of the cavity 14 which are diametrally opposite one another, so that they engage the member 13 at diametrally opposite sides. The diameter of the piston 16 is approximately twice as great as the piston 15, so that the pistons act as differential pistons. Two fluid passages 19 and 20 communicate with the cavity 14. For purposes of explanation it will be assumed that the rotor 11 turns in the direction indicated by the arrow that the passage 19 represents the high pressure side and the passage 20 the low pressure side of the machine 10. The high pressure side 19 may communicate with a user such as a hydraulic motor that is preferably connected in a closed circuit with the machine 1 1, so that a hydrostatic drive having a closed circuit exists. The low pressure side 20 may communicate with a low pressure space, such as a reservoir.

A fluid conduit 21 extends from the low pressure pressure side or passage 20 to the high pressure side 19 and has a switching valve 22 accommodated, composed of a valve body 24 which cooperates either with one or the other of two valve seats 23, 23, so that each valve seat together with the valve body 24 constitutes a oneway valve blocking flow in one or the other direction in the conduit 21. a conduit 25 branches off the conduit 21 at a location which is midway between the two valve seats 23, 23' and leads to the bore 17 for the piston 15, and also to a four port three-position valve 26 which is movable between three positions I, II and III. The conduit 25 continues beyond the valve 26 to a servo-control unit 27 which in principle is configurated as a three-port three-position valve 27' which can be moved at will by means of a lever, a magnet or the like, into one of its switching positions I, II or III. A further fluid passage extends from the valve 27 via the valve 26 to the fluid reservoir 29, and another fluid passage 30 extends from the valve 27' to a fluid passage 31 which communicates with the bore 18 in which the piston 16 is slidable and also to a relief valve 32 which is constructed as a two-port two-position valve having switching positions I and II. The conduit 31 extends beyond the valve 32 and communicates with the conduit 21. At one side the valve member of the valve 32 is biased by a spring 33, and at the opposite side it is biased by fluid acting upon it from a fluid line 34 which communicates with the line 25. Springs 35 and 36 act upon the opposite ends of the valve member of the valve 26 and maintain it normally in the center position II. In addition, a conduit 37 which communicates with the fluid line 20, also communicates with that end face of the valve member of the valve 26 which is engaged by the spring 35. A conduit 38, branching off the fluid line 19, communicates with the opposite end face of the valve member in the valve 26, namely the end face which is engaged by the spring 36. The valve member in the valve 27' of the servo-control unit 27 is also engaged at its opposite ends by springs 39 and 40, respectively. In addition, it is connected with the piston 16 in a mechanical sense, namely in the illustrated embodiment via a rod 41 so that the piston 16 and the valve member of the valve 27 move in unison. A spring 42 is located in the bore 18 and biases the piston 16, and a similar spring 43 is located in the bore 17 and biases the piston 15.

When the pump is to operate and supply fluid into the high pressure fluid line 19 and from there to the user, the valve 27' of the servo-control unit 27 must be in the position III thereof. The member 13 is mechanically shifted slightly in upward direction out of its zero position, counter to the action of the piston 16. The pump is now capable of forcing pressure fluid into the fluid line 19 and the pressure which develops therein is communicated via the line 21 and the valve 23', 24 which opens under this pressure into the conduit 25. The valve member 24 at this time is in sealing engagement with the valve seat 23.

The pressure existing in the fluid line 19 also is communicated via the conduit 38 to the valve 26 which is in the position 11, so that pressure fluid can travel via the fluid line 25 to the valve 27 The pressure in the bore 17 is the unthrottled pump pressure so that, as the pressure rises, the piston is moved upwardly counter to the force exerted by the piston 16, despite the fact that its surface area is smaller than that of the piston 16; this results in a displacement of the member 13 in a sense permitting an increased flow of fluid through the pump per unit time, until finally the maximum pumping position is reached which is shown in the drawing.

When the pump pressure reaches a predetermined maximum upper limit, the valve 32 is moved to its position I by the pressure which obtains in the conduit 34 which is in communication with the conduit 35; this movement takes place counter to the biasing force of the spring 33 and permits the unthrottled flow of pressure fluid via the conduit 2 1 and 31 into the bore 18. At this time, identical pressure is operative in the bores 17 and 18 upon the pistons 15 and 16, respectively. However, since the surface area of the piston 16 is greater than that of the piston 15, the piston 16 is able to overcome the force exerted by the piston 15 and the mem- 4 ber 13 is shifted (downwardly in the drawing) to towards its center position.

The inward movement of the piston 16, that is downwardly in the drawing, causes a displacement of the valve member of the valve 27 which is mechanically coupled with it to a position which is midway between the positions II and III and this would inherently permit pressure fluid to flow out of the bore 18 and into the conduit 30 and via the conduit 28 to the reservoir 29. If that were to be permitted, the piston 15 would immediately be able to re-adjust the pump to a higher throughput rate, which is not desired. The valve 26 which is provided in accordance with the present invention avoids this problem.

Shortly before the pressure is reached which is capable of switching the valve 32, the valve 26 is shifted by the fluid pressure acting in the line 38 out of its position II and into its position III in which it blocks the flow of pressure fluid from the bore 18 via the line 28 to the reservoir 29. The servo-control unit 27 can now, when the valve 27' thereof is in a position located midway between the positions I and II, permit high pressure fluid from the line 28 to enter into the bore 18 and to continue to act upon the piston 16 in a sense shifting the member 13 to a position in which the flow through rate through the pump is reduced, and the pressure fluid is consequently also reduced.

If the machine 10 is connected in a closed circuit with a hydraulic motor and the latter itself operates as a pump, then the machine 10 will self-evidently be operating as a motor. In such a case, the machine 10 receives high pressure fluid from the user via the fluid line 20. In other words, in this type of operation the high and low pressure sides will be reversed and the fluid line 19 will now be the low pressure side. If in such operation the maximum pressure value is reached at the valve 32 moves to its position I, then the bore 18 is connected with the now low pressure line 19 via the line 31 and the valve 32 as well as the line 21. The high pressure acting in the line 20 presses the valve member 24 against the valve seat 23', lifting it off the valve seat 23, so that the pressure acting in the bore 17 can shift the member 13 upwardly against the force of the piston 16, and adjust the machine (which now operates as a motor) for a higher flowthrough per unit time. Shortly before the valve 32 switches the valve 26 has been shifted to position I by the pressure prevailing in the conduit 37 and blocks the line 25, whereas the line 28 continues to be in communication with the reservoir 29. This makes it possible for the servo-control unit 27 and the valve 27 thereof to continue to be moved in a sense permitting an increased fluid flow per unit time.

Merely by way of example it is pointed out that the pump 10 or motor 10, depending upon the manner in which it is operated, can also be so constructed that it can be reversible, that is that it can be adjustable +Q via zero to -Q a1. In this case, also, the arrangement according to the present invention will be fully effective.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a hydraulic system, it is not intendedto be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the prescut invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications, without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A hydraulic system, comprising a variable-flow fluid-handling machine having a high-pressure side and a low-pressure side and an adjusting member which is movable between a plurality of flow-adjusting positions; a larger and a smaller piston acting upon said member in mutually opposite directions, said smaller piston being connected in circuit with said high-pressure side; a multi-position servo-control unit to which said larger piston is mechanically connected so as to share the movements thereof, said unit connected in circuit with said machine and including a relief valve in circuit with said larger piston and said machine for controlling the flow of fluid from said high-pressure side when the fluid pressure exceeds a preset limit; and a control valve connected with said high-pressure side and said unit and operative at a pressure slightly below said preset limit for moving said unit to a position in which said unit connects said larger piston with said high-pressure side and interrupts communication of said larger piston with a low-pressure space.

2. A hydraulic system as defined in claim 1, wherein said large piston is connected to said unit by connecting means comprising a mechanical linkage.

3. A hydraulic system, comprising a variable-flow fluid-handling machine which is operable at will as a pump or as a hydraulic motor, said machine having a high-pressure side and a low-pressure side and an adjusting member which is movable between a plurality of flow-adjusting positions; a larger and a smaller piston acting upon said member in mutually opposite directions, said smaller piston being connected in circuit with said high-pressure side; a multi-position servocontrol unit to which said larger piston is mechanically connected so as to share the movements thereof, said unit connected in circuit with said machine and including a relief valve in circuit with said larger piston and said machine for controlling the flow of fluid from said high-pressure side when the fluid pressure exceeds a preset limit; and a four-port three-position slide control valve being operable in both modes of operation of said machine and being connected with said high-pressure side and said unit and operative at a pressure slightly below said preset limit for moving said unit to a position in which said unit connects said larger piston with said high-pressure side and interrupts communication of said larger piston with a low-pressure space.

4. A hydraulic system as defined in claim 1, wherein said fluid-handling machine is a pump.

5. A hydraulic system as defined in claim 1 wherein said fluid-handling machine is a sliding-vane pump.

6. A hydraulic system as defined in claim 1, said machine being selectively operable as a pump or a motor; and further comprising a switching valve connected in circuit with and located between said high-pressure side and said low-pressure side, for at times connecting said high-pressure side to said relief valve and said control valve irrespective of whether said machine operates as a pump or as a motor. 

1. A hydraulic system, comprising a variable-flow fluid-handling machine having a high-pressure side and a low-pressure side and an adjusting member which is movable between a plurality of flowadjusting positions; a larger and a smaller piston acting upon said member in mutually opposite directions, said smaller piston being connected in circuit with said high-pressure side; a multiposition servo-control unit to which said larger piston is mechanically connected so as to share the movements thereof, said unit connected in circuit with said machine and including a relief valve in circuit with said larger piston and said machine for controlling the flow of fluid from said high-pressure side when the fluid pressure exceeds a preset limit; and a control valve connected with said high-pressure side and said unit and operative at a pressure slightly below said preset limit for moving said unit to a position in which said unit connects said larger piston with said high-pressure side and interrupts communication of said larger piston with a low-pressure space.
 2. A hydraulic system as defined in claim 1, wherein said large piston is connected to said unit by connecting means comprising a mechanical linkage.
 3. A hydraulic system, comprising a variable-flow fluid-handling machine which is operable at will as a pump or as a hydraulic motor, said machine having a high-pressure side and a low-pressure side and an adjusting member which is movable between a plurality of flow-adjusting positions; a larger and a smaller piston acting upon said member in mutually opposite directions, said smaller piston being connected in circuit with said high-pressure side; a multi-position servo-control unit to which said larger piston is mechanically connected so as to share the movements thereof, said unit connected in circuit with said machine and including a relief valve in circuit with said larger piston and said machine for controlling the flow of fluid from said high-pressure side when the fluid pressure exceeds a preset limit; and a four-port three-position slide control valve being operable in both modes of operation of said machine and being connected with said high-pressure side and said unit and operative at a pressure slightly below said preset limit for moving said unit to a position in which said unit connects said larger piston with said high-pressure side and interrupts communication of said larger piston with a low-pressure space.
 4. A hydraulic system as defined in claim 1, wherein said fluid-handling machine is a pump.
 5. A hydraulic system as defined in claim 1 wherein said fluid-handling machine is a sliding-vane pump.
 6. A hydraulic system as defined in claim 1, said machine being selectively operable as a pump or a motor; and further comprising a switching valve connected in circuit with and located between said high-pressure side and said low-pressure side, for at times connecting said high-pressure side to said relief valve and said control valve irrespective of whether said machine operates as a pump or as a motor. 